72 BYZANTINE CHURCHES CHAP. from the ioor to the springing of the dome arches. The archways thus formed, except the bema arch3 are filled in with two pairs of columns in two stories set on the outer plane of the piers. The lower colonnade is surmounted, after the classic fashion, by a horizontal entablature profusely carved ; while the upper columns are bound by arches, thus making seven sides of the octagon a beautiful open screen of fourteen columns and as many triple arcades, resplendent with marbles of various hues and rich with carved work. The mass of the piers is relieved by their polygonal form, a fluted cymatium along their summit, and a repeating design of a flower between two broad leaves below the entablature* Though the flower points upwards It has been mistaken for a cluster of grapes.1 At the four diagonal points the sides of the octagon are semicircular,, forming exhedrae, an arrangement which gives variety to the lines of the figure, widens the central area, secures more frontage for the gallery, and helps to buttress the dome. The same feature appears in S. Sophia, whereas in San Vitale all the sides of the octagon, excepting the eastern side, are semicircular. The extension of the interior area of a building (square or octagonal) by means of niches at the angles or in the sides, or both at the angles and in the sides, was a common practice.2 There is considerable difference in the size of the piers and the dome arches. The eastern piers stand farther apart than their companions, and consequently the arch over them, the triumphal arch of the sanctuary, is wider and loftier than the other arches. The bays to the north-east and the southeast are also wider than the bays at the opposite angles. The apse is semicircular within, and shows three sides on the exterior. As in S, Sophia and S. Irene, there is no prothcsis or diacomcon. The pairs of columns, both below and above, are 1 Gyllius, Df Top. C,P. ii. c. 16. If the design represented vine leaves ami grapes, it surely did not allude to the god Bacchus, hut to the vine In the gospel of S, John. 1 he small columns on the piers are Turkish. <J Antotttadi, *Sf, Sophia^ vol* II. pp. 7-9, draws attention to the development of buildings with sides turned Into exhedrae, from their Amplest form to their culmination in S. Sophia, He refers for illustrations to plans in Dehlo und Bezold, Die kiwJillehe Bmtkumt ties Ahendlandes9 vol. I, "pp. 353-31 j Atlas, vol, i plate I, figures i» *, 3» 4* 7 5 plate in, figures i, 2, 7.